英文文獻-基于單片機的大棚溫濕度控制系統(tǒng)的設(shè)計-在線瀏覽
2024-12-22 15:15本頁面
【正文】 t range develops, since successive enhancements may bee too big for onchip memory and it is undesirable not to build on the existing software base. Serial input/output . Serial munication with terminal devices is mon means of providing a link using a small number of lines. This sort of munication can also be exploited for interfacing special function chips or linking several microputers together .Both the mon asynchronous synchronous munication schemes require protocols that provide framing (start and stop) information .This can be implemented as a hardware facility or U(S) ART(Universal(synchronous) asynchronous receiver/transmitter) relieving the processor (and the applications programmer) of this lowlevel, timeconsuming, detail. t is merely necessary to selected a baudrate and possibly other options (number of stop bits, parity, etc.) and load (or read from) the serial transmitter (or receiver) buffer. Serialization of the data in the appropriate format is then handled by the hardware circuit. Timing/counter facilities. Many application of singlechip microputers require accurate evaluation of elapsed real time .This can be determined by careful assessment of the execution time of each branch in a program but this rapidly bees inefficient for all but simplest programs .The preferred approach is to use timer circuit that can independently count precise time increments and generate an interrupt after a preset time has elapsed .This type of timer is usually arranged to be reloadable with the required count .The timer then decrements this value producing an interrupt or setting a flag ， when the counter reaches zero. Better timers then have the ability to automatically reload the initial count value. This relieves the programmer of the responsibility of reloading the counter and assessing elapsed time before the timer restarted ,which otherwise wound be necessary if continuous precisely tim
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